Clients use the security mechanism to ensure a secure pathway to a remote server. Replication Server logs in to remote servers (acting as a client) and also accepts incoming logins (acting as a server). How security services work depends on whether Replication Server (or Adaptive Server or other data server) is acting as client or server.
Replication Server, when acting as the client, uses the security mechanism to ensure a secure pathway to a remote Replication Server or Adaptive Server. Once the secure pathway is established, the security mechanism can provide message protection. When Replication Server acts as a server, it accepts or rejects logins based on its default security settings.